JP2005024991A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which an image carrier having a single layer type organic photosensitive layer can be contact-charged under actual operating conditions accompanied by environmental variation, while preventing damage of the organic photosensitive layer without impairing uniformity of charge or charge efficiency. <P>SOLUTION: The image forming apparatus is provided with the image carrier 1, a charging member 2 for contact-charging the image carrier 1, a bias power source 8 which generates bias by superposing DC voltage and AC voltage and applies the bias to the charging member 2, a sensor 9 for sensing temperature and humidity, and CPU (central processing unit) 11 for controlling the bias power source 8. This CPU adjusts positive component domains A and negative component domains B of the AC voltage to a ratio corresponding to sensed results from the sensor 9, with respect to the bias, while keeping voltage value of the DC voltage and peak voltage value of the AC voltage constant. A percentage of the positive component domains A is set so that it is made lower in accordance with increase of the sensed results as against standard levels and it is made higher in accordance with decrease of the sensed results as against the standard levels. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile, and more particularly to an image forming apparatus that charges an organic photosensitive layer on the surface of an image carrier by a so-called contact charging method.
[0002]
[Prior art]
In a conventional general image forming apparatus, the following image forming operation is generally performed. First, the surface of the photosensitive drum as an image carrier is uniformly charged to a predetermined potential by a charger. Next, an electrostatic latent image is formed on the surface of the photosensitive drum by the irradiation light based on the image information from the exposure device, and toner is attached to the electrostatic latent image by the developing device to develop the visible toner image. Subsequently, the visible toner image on the photosensitive drum is transferred onto a sheet material such as paper by a transfer device such as a transfer roller. Thereafter, the sheet material is conveyed to a fixing device composed of a pair of rollers, and a toner image is fixed by heating and pressurization in the fixing device, and is discharged or outputted to the outside. On the other hand, the toner remaining on the surface of the photosensitive drum after transfer is removed by a cleaning device such as a cleaning blade, and the surface of the photosensitive drum is uniformly discharged by a static eliminator as necessary. Such an image forming operation is repeated.
[0003]
Here, as a method for charging the photosensitive drum, there are a so-called non-contact charging method and a contact charging method. A typical corona charger is a charger in an image forming apparatus that employs the former non-contact charging method, and this corona charger generates a discharge corona toward a photoconductor drum disposed oppositely at a small interval. Thus, the surface of the photosensitive drum is charged. However, this corona charger has disadvantages that discharge products such as ozone that is harmful to the environment and ammonium salts that accelerate the surface deterioration of the photosensitive drum and adversely affect the image quality are generated.
[0004]
On the other hand, in the latter contact charging method, a conductive charging member to which a bias formed by superimposing a DC voltage and an AC voltage is applied is brought into contact with the surface of the photosensitive drum, whereby the contact charging member is passed through the contact charging member. Charge is applied to the surface of the photosensitive drum, and the surface is charged (for example, see Patent Document 1). Image forming apparatuses that employ this contact charging method have become the mainstream in recent years because they can significantly reduce the generation of discharge products. The bias applied to the contact charging member is formed by superimposing a DC voltage and an AC voltage, which is applied in order to increase the charging uniformity and charging efficiency for the photosensitive drum. Hereinafter, an image forming apparatus employing this contact charging method will be described.
[0005]
Incidentally, an image carrier (photosensitive drum) in an image forming apparatus is particularly expensive among components mounted on the apparatus. Therefore, in recent years, for the purpose of reducing costs, an organic photosensitive layer has been adopted as a substantially charged photosensitive layer, and this organic photosensitive layer is formed as a single layer or a laminated layer on the surface of a conductive element tube. A carrier is used. A single-layer organic photosensitive layer is obtained by dispersing a charge generating agent and a charge transporting agent in a binder resin, and a laminated organic photosensitive layer has a charge generating agent and a charge transporting agent dispersed in separate layers. The charge generation layer containing the charge generation agent is coated with the charge transport layer containing the charge transfer agent. An image carrier having an organic photosensitive layer has the following characteristics and problems associated therewith.
[0006]
First, it is sensitive to environmental changes such as temperature and humidity during use, and the charging characteristics of the organic photosensitive layer change remarkably following the environmental changes. That is, as shown in FIG. 7, as the temperature and humidity increase, the chargeability of the organic photosensitive layer (the degree of charge with respect to a given bias) increases. Then, if a bias set in advance to meet the standard condition is always applied to the contact charging member under the same setting conditions, the bias applied to the organic photosensitive layer is excessive if the temperature or humidity is higher than the standard level. As a result, the surface potential of the organic photosensitive layer is increased. On the other hand, when the temperature and humidity are lower than the standard level, the organic photosensitive layer is not charged to a desired predetermined potential. In either case, the quality of the image finally formed on the sheet material is reduced.
[0007]
Secondly, the surface of the organic photosensitive layer is likely to be worn or deteriorated due to contact with the charging member or the application of a bias due to repeated use, particularly following changes with time such as a decrease in the thickness of the organic photosensitive layer. As a result, the chargeability of the organic photosensitive layer gradually decreases (see FIG. 8). That is, if a bias set in advance so as to match the initial state is permanently applied to the contact charging member under the same setting conditions, the organic photosensitive layer is not charged to a desired predetermined potential. As a result, the image quality on the sheet material is gradually lowered.
[0008]
As described above, for an image carrier having an organic photosensitive layer, it is necessary to appropriately adjust the bias applied to the contact charging member in accordance with an environmental change and a change with time in consideration of actual usage conditions. Therefore, in the past, the DC voltage value (hereinafter, sometimes referred to as “DC voltage value”) among the DC voltage and AC voltage, which are the components of the bias, is adjusted, or the peak voltage value of the AC voltage ( Hereinafter, it may be referred to as “AC peak voltage value”). In other words, with regard to environmental changes, when the temperature and humidity are higher than the standard level, the DC voltage value or the AC peak voltage value is reduced with respect to the standard condition setting conditions, while the temperature and humidity are lower than the standard level. In this case, the DC voltage value or the AC peak voltage value was increased with respect to the standard condition setting conditions. Regarding the change over time, the DC voltage value or the AC peak voltage value was increased with respect to the initial setting conditions as the thickness of the organic photosensitive layer decreased with respect to the initial level.
[0009]
[Patent Document 1]
JP-A-6-202434
[0010]
[Problems to be solved by the invention]
However, in any adjustment of the DC voltage value or the AC peak voltage value, pinholes or the like are formed in the organic photosensitive layer of the image bearing member at a low temperature or low humidity due to environmental changes or in a state where the film thickness of the organic photosensitive layer is reduced. It may occur. This is because the maximum peak voltage value of the bias itself increases as the DC voltage value or the AC peak voltage value increases, which is effective for the chargeability of the organic photosensitive layer, but the organic photosensitive layer can withstand. This is an excessive bias. In addition, in the adjustment of the AC peak voltage value under high temperature and high humidity, the peak voltage value of the bias itself decreases as the AC peak voltage value decreases, so the AC voltage is applied to the DC voltage as a bias. The superimposed effect is weakened, and the uniformity of charging and the charging efficiency with respect to the image carrier are deteriorated.
[0011]
Therefore, for an image carrier having an organic photosensitive layer, the bias applied to the contact charging member needs to be appropriately adjusted in accordance with environmental changes and changes with time, but the bias DC voltage value or AC peak voltage value. It can be said that this adjustment cannot be adequately addressed.
[0012]
Therefore, the present invention has been made in view of the above problems, and an organic photosensitive layer is used for an image carrier having a single organic photosensitive layer under actual usage conditions accompanied by environmental changes and changes over time. It is an object of the present invention to provide an image forming apparatus which can prevent contact damage and can perform contact charging without impairing charging uniformity and charging efficiency.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, an image forming apparatus according to the present invention includes an image carrier having an organic photosensitive layer on the surface, and a contact charging member that contacts the surface of the image carrier and charges the organic photosensitive layer to a predetermined potential. And a bias applying unit that generates a bias formed by superimposing a DC voltage and an AC voltage and applies the bias to the contact charging member, in an ambient temperature or humidity of the image carrier. A sensor for detecting at least one; and a control means for controlling the bias applying means based on a detected temperature or humidity detected from the sensor, wherein the control means relates to the bias, and While maintaining the voltage value and the peak voltage value of the AC voltage constant, the positive component region and the negative component region in the waveform of the AC voltage are adjusted to a ratio corresponding to the detection result. The ratio of the component region having the same polarity as the charged polarity of the image carrier is set to be smaller as the detection temperature or detection humidity is higher, and is set to be larger as the detection temperature or detection humidity is lower. It is characterized by being.
[0014]
As a result, the effective peak voltage value is adjusted to be larger at low temperatures and low humidity compared to the standard level, and smaller at high temperatures and high humidity, while the maximum peak voltage value of the bias itself is kept constant. The Therefore, under low temperature and low humidity, it is possible to give an effective superimposing bias for the uniformity of charging and charging efficiency to the organic photosensitive layer having reduced chargeability, and the bias damages the organic photosensitive layer. Is not enough to give On the other hand, even at high temperatures and high humidity, it is possible to give a superimposing bias effective for charging uniformity and charging efficiency to an organic photosensitive layer having improved charging properties.
[0015]
An image forming apparatus according to the present invention for achieving the above object includes an image carrier having an organic photosensitive layer on the surface, and a contact for contacting the surface of the image carrier and charging the organic photosensitive layer to a predetermined potential. An image forming apparatus comprising: a charging member; and a bias applying unit that generates a bias formed by superimposing a DC voltage and an AC voltage and applies the bias to the contact charging member, and detects an index of the thickness of the organic photosensitive layer And a control means for controlling the bias applying means based on a detection result from the thickness index detecting means. The control means relates to the bias, and While maintaining the voltage value and the peak voltage value of the alternating voltage constant, the positive component region and the negative component region in the waveform of the alternating voltage are calculated based on the thickness of the organic photosensitive layer calculated from the detection result. Being adapted to adjust the ratio of response, the ratio of the same polarity as the charge polarity of the component region of the image bearing member is characterized by being larger set according to the thickness decrease.
[0016]
As a result, while the maximum peak voltage value of the bias itself is maintained constant, the effective voltage value is adjusted to be larger as the thickness of the organic photosensitive layer is decreased from the initial level. Therefore, it is possible to apply an effective superimposing bias to the uniformity of charging and charging efficiency to the organic photosensitive layer whose charging property is gradually decreased due to the decrease in film thickness, and the bias is damaged to the organic photosensitive layer. Is not enough to give
[0017]
Here, since it is difficult to directly measure the thickness of the organic photosensitive layer, the thickness is calculated indirectly through the thickness index calculation means. For this purpose, it is preferable that the thickness index detecting means detects the cumulative number of sheet materials formed and output by the image forming apparatus as the index. Further, the thickness index detection means may detect the current amount of the bias flowing into the contact charging member from the bias application means as the index.
[0018]
Furthermore, in view of practicality, the contact charging member is preferably in the form of a roller or a brush.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of an image forming apparatus of the present invention will be described in detail with reference to the drawings. FIG. 1 is a longitudinal sectional view showing a main part of an image forming apparatus according to an embodiment of the present invention, and FIG. 2 is a schematic diagram of an AC voltage waveform in a bias used in the image forming apparatus. ) Is a state where the ratio of the positive component region and the negative component region of the AC voltage is equal, FIG. 2B is a state where the ratio of the positive component region is large, and FIG. 2C is a state where the ratio of the positive component region is small. Each is shown. 3 is a data table showing an example of the ratio of positive component areas corresponding to environmental changes, FIG. 4 is a schematic diagram showing the correlation between the cumulative number of sheets output and the thickness of the organic photosensitive layer, and FIG. FIG. 6 is a flowchart for explaining an image forming operation in the image forming apparatus.
[0020]
The image forming apparatus according to the present embodiment employs a contact charging method. As shown in FIG. 1, the image forming apparatus is largely a photosensitive drum 1 that is an image carrier that is driven to rotate about an axis, and the photosensitive drum. A charging member 2 that uniformly charges the surface of 1 to a predetermined potential; an exposure unit 3 that exposes the surface of the photosensitive drum 1 charged by the charging member 2 to form an electrostatic latent image based on image information; The developing device 4 for forming (developing) a toner visible image by attaching toner to the electrostatic latent image formed by the exposure device 3, and the toner visible image formed by the developing device 4 as a sheet material P A transfer device 5 composed of a transfer roller to be transferred to the surface, a cleaning device 6 for removing the toner remaining on the surface of the photosensitive drum 1 after the transfer, and a toner image transferred on the sheet material P is heated and pressurized. A fixed pair of rollers It includes a vessel 7, the.
[0021]
Further, a bias power source 8 that generates a bias in which a DC voltage and an AC voltage are superimposed, a sensor 9 that detects the temperature and humidity around the photosensitive drum 1 in the apparatus, and an image formed by the apparatus. A counter 10 that measures the accumulated number of sheet materials P that are output, and a CPU 11 that is connected to the bias power source 8, the sensor 9, and the counter 10 and controls the whole are provided.
[0022]
More specifically, the photosensitive drum 1 is formed by forming an organic photosensitive layer 1b as a single layer on the surface of a conductive element tube 1a such as aluminum as a base. It contacts a conductive rubber layer 2b, which will be described later, and is substantially charged and charged to a predetermined potential.
[0023]
Here, the detailed structure of the organic photosensitive layer 1b will be described. The organic photosensitive layer 1b is formed by dispersing a charge generating agent (CGM) and a charge transporting agent (CTM) in a binder resin. As the charge generating agent, phthalocyanine pigments, perylene pigments, and the like are suitable. However, selenium, selenium-tellurium, amorphous silicon, or the like may be used, and two or more kinds may be mixed so as to have an absorption wavelength region in a desired region. Can also be used. As the charge transport agent, it is preferable to use a combination of a known electron transport agent (ETM) and a hole transport agent (HTM).
[0024]
Examples of the electron transporting agent include electron-withdrawing substances such as succinic anhydride, maleic anhydride, and dibromosuccinic anhydride, and two or more kinds can be used in combination. On the other hand, examples of the hole transporting agent include pyrene, a carbazole compound, a hydrazone salt, and the like, and two or more of them can be used in combination. As the binder resin, a polycarbonate resin, a polyester resin, or the like is preferable in terms of excellent wear resistance.
[0025]
In the organic photosensitive layer 1b of the present embodiment, the charge generating agent is contained at 3 to 5% by weight per solid and the charge transporting agent is contained at about 60 to 80% by weight per solid, and the electron transporting agent and the hole transporting agent are contained. The weight ratio is about 1: 5 to 1: 1. The initial thickness of the organic photosensitive layer 1b is generally about 25 to 100 μm, but in this embodiment, it is set to 30 μm.
[0026]
Regarding the method of forming the single-layer organic photosensitive layer 1b on the conductive element tube 1a, a coating solution in which a charge generating agent, a charge transporting agent and a binder resin are dissolved or dispersed in an appropriate solvent at a predetermined quantitative ratio is used. This is carried out by preparing, coating the conductive elemental tube 1a with a predetermined thickness by dipping or the like, and drying it by heating.
[0027]
However, the organic photosensitive layer 1b may be formed directly on the conductive element tube 1a, but an undercoat layer may be interposed between the two. Examples of the undercoat layer include polymer films such as casein and polyvinyl alcohol, and the thickness is preferably about 0.01 to 20 μm. In this case, in order to impart conductivity to the undercoat layer, a metal powder such as gold, silver or aluminum, a metal oxide powder such as titanium oxide or tin oxide, or a conductive fine powder such as carbon black may be dispersed. Is preferred.
[0028]
In addition, an overcoat layer may be provided on the surface of the organic photosensitive layer 1b in consideration of the further uniformity of charging and the peelability of the adhered toner with respect to the organic photosensitive layer 1b. As this overcoat layer, it is required to be transparent and to have excellent wear resistance, toner release properties and the like, and a silicon resin is optimal. The thickness is preferably about 0.5 to 5 μm in consideration of the ease of molding and the chargeability of the organic photosensitive layer 1b.
[0029]
Subsequently, the charging member 2 is formed by forming a conductive rubber layer 2b on the surface of the roller-shaped conductive base 2a, and is disposed to face the surface of the photosensitive drum 1 in an elastic contact state. The motor rotates in synchronization with the rotation of the motor. Here, the conductive substrate 2 a is made of metal such as aluminum, steel, or stainless steel, and is connected to the bias power source 8. The conductive rubber layer 2b is an ion conductive rubber composition in which conductive powders such as carbon black and metal powder are dispersed in various rubbers such as epichlorohydrin rubber, silicon rubber, polybutadiene rubber and acrylic rubber. A bias from the bias power source 8 according to a command from the CPU 11 is applied to the conductive rubber layer 2b through the conductive base 2a. The detailed nature of this bias will be described later.
[0030]
The reason why the elastic conductive rubber layer 2b is provided is to maintain stable contact of the photosensitive drum 1 as a contact target with the organic photosensitive layer 1b. Therefore, instead of the conductive rubber layer 2b, a conductive brush that acts in the same manner may be provided so as to protrude from the surface of the conductive substrate 2a.
[0031]
Subsequently, the nature of the bias applied to the charging member 2 and its adjustment will be described in detail. In the present embodiment, the temperature and humidity that are detection results from the sensor 9 for environmental changes, that is, the environmental outputs, and the cumulative output of the sheet material P that is the detection results from the counter 10 for temporal changes. The bias is adjusted by the CPU 11 based on the number of sheets. The bias adjustment is performed by changing the ratio between the positive component region A and the negative component region B in the sine wave that is the waveform of the alternating voltage that is a component of the bias, as shown in FIG. However, the voltage value of the DC voltage and the peak voltage value Vpp of the AC voltage are kept constant. Here, the positive component region A indicates an area on the plus side of the median value between peaks (0 (zero) in FIG. 2) in the waveform of only the alternating voltage, and the negative component region B is minus. The median value between the peaks corresponds to the voltage value of the DC voltage in the actual bias.
[0032]
Next, regarding the ratio between the positive component region A and the negative component region B, first, regarding the environmental change, a specific ratio is determined in advance for each temperature and humidity. An example is shown in FIG. Here, the temperature is 15 to 25 ° C. and the humidity is 20 to 80% as a standard level, and the ratio of the positive component area A at this standard level is 50% (the ratio of the negative component area B is also 50%). That is, in the waveform at the standard level, the positive component region A and the negative component region B are equally symmetrical as shown in FIG.
[0033]
Further, for example, when the temperature is 15 ° C. or lower and the humidity is 20% or lower under a low temperature and low humidity with respect to the standard level, the ratio of the positive component region A is set to 70% larger than the standard level (the proportion of the negative component region B is 30%). Yes. In the waveform under the low temperature and low humidity, the positive component region A is more asymmetrical than the negative component region B as shown in FIG. That is, under low temperature and low humidity, the effective voltage value is adjusted to be larger while maintaining the maximum peak voltage value constant as compared with the standard level when viewed from the bias itself.
[0034]
On the other hand, when the temperature is 25 ° C. or higher and the humidity is 80% or higher under high temperature and high humidity with respect to the standard level, the ratio of the positive component region A is 30% smaller than the standard level (the proportion of the negative component region B is 70%). Yes. In this waveform under high temperature and high humidity, the positive component region A is smaller than the negative component region B and is asymmetric as shown in FIG. In other words, under high temperature and high humidity, the effective voltage value is adjusted to be smaller while maintaining the maximum peak voltage value constant as compared with the standard level when viewed from the bias itself.
[0035]
As described above, the ratio of the positive component region A used for adjustment of the bias related to the environmental change is determined to be smaller as it becomes higher than the standard level and larger as it becomes lower than the standard level. .
[0036]
On the other hand, the ratio between the positive component area A and the negative component area B with respect to change over time is uniquely determined in advance for each thickness of the organic photosensitive layer 1 b of the photosensitive drum 1. Here, since it is difficult to directly measure the thickness of the organic photosensitive layer 1b, the cumulative number of output sheets of the sheet material P is used as an indicator of the change in thickness. This utilizes the fact that the thickness of the organic photosensitive layer 1b generally decreases in proportion to the progress of image formation by the apparatus. For example, as shown in FIG. 4, the initial thickness of 30 μm is halved when the cumulative output number is about 100,000.
[0037]
Returning to the description, FIG. 5 shows an example of the ratio of the positive component region A and the negative component region B regarding the change with time. Here, the cumulative number of sheets up to 35,000 is the initial level, and the ratio of the positive component area A at this initial level is 50% (the ratio of the negative component area B is also 50%). That is, in the waveform at the initial level, the positive component region A and the negative component region B are equally symmetric as shown in FIG.
[0038]
Further, for 35,000 to 70,000 sheets in which the thickness of the organic photosensitive layer 1b has decreased with respect to the initial level, the ratio of the positive component area A is 55% larger than the initial level (the ratio of the negative component area B is 45%). Further, in 70,000 to 100,000 sheets that have advanced further, the ratio of the positive component area A is set to 60% (the ratio of the negative component area B is 40%). In both waveforms, the positive component region A is larger and asymmetrical than the negative component region B as shown in FIG. In other words, as the thickness of the organic photosensitive layer 1b decreases with respect to the initial level, the effective voltage value is adjusted to be larger while the maximum peak voltage value is maintained constant when viewed from the bias itself. ing.
[0039]
As described above, the ratio of the positive component region A used for adjusting the bias with respect to the change with time is determined to increase as the thickness of the organic photosensitive layer 1b decreases with respect to the initial level.
[0040]
Next, an image forming operation in the image forming apparatus will be described. As shown in FIG. 6, when the image forming operation is started, the CPU 11 receives the temperature and humidity detected by the sensor 9 (step # 10). At the same time, the output cumulative number of sheets P detected so far by the counter 10 is received (step # 20), and the current thickness of the organic photosensitive layer 1b on the photosensitive drum 1 is calculated from this cumulative number. (Step # 30).
[0041]
Next, in step # 40, an adjustment amount (a ratio of the positive component region A) between the positive component region A and the negative component region B of the alternating voltage that is a component of the bias is determined. Specifically, the ratio of the positive component region A corresponding to the temperature and humidity acquired from the sensor 9 is extracted from the data table shown in FIG. 3, and the calculated organic photosensitive layer 1b is calculated from the data table shown in FIG. The ratio of the positive component region A corresponding to the thickness is extracted, and these extracted ratios are integrated to obtain a bias adjustment amount.
[0042]
Subsequently, in step # 50, this adjustment amount is given to the bias power source 8, and the bias power source 8 adjusts the AC voltage in accordance with the adjustment amount, and a bias in which the AC voltage and the DC voltage are superimposed is charged. 2 is applied.
[0043]
In step # 60, contact charging, exposure, and development of the photosensitive drum 1 with respect to the organic photosensitive layer 1b are performed, and toner image transfer and fixing are performed on the sheet material P. Subsequently, Thus, the organic photosensitive layer 1b is cleaned. This completes one cycle of image forming operation.
[0044]
In such an image forming operation, the bias applied to the charging member 2 maintains its maximum peak voltage value constant, and its effective voltage value is lower than that of the standard level at a lower temperature or lower humidity. It is larger and on the other hand, it is adjusted smaller under high temperature and high humidity. Therefore, under low temperature and low humidity, it is possible to apply a superimposing bias effective for charging uniformity and charging efficiency to the organic photosensitive layer 1b having reduced chargeability, and the bias is applied to the organic photosensitive layer 1b. It will not be damaged. On the other hand, a superimposing bias effective for charging uniformity and charging efficiency can be applied to the organic photosensitive layer 1b having improved chargeability even under high temperature and high humidity.
[0045]
Further, the effective voltage value of the bias itself is adjusted to be larger as the thickness of the organic photosensitive layer 1b is decreased from the initial level. For this reason, it is possible to give a superimposing bias effective for charging uniformity and charging efficiency to the organic photosensitive layer 1b whose charging property is gradually lowered due to the decrease in film thickness, and the bias is applied to the organic photosensitive layer. It is not enough to damage 1b.
[0046]
Therefore, the quality of the image finally formed on the sheet material P is excellent regardless of environmental changes and changes with time.
[0047]
In addition, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, the detection target for adjusting the bias related to the environmental change is desirably both temperature and humidity as in the above-described embodiment, but any one of temperature and humidity is used depending on the region of use. It is also possible to make it. Furthermore, in the above-described embodiment, both environmental changes and temporal changes are detected and adjusted to a bias that takes into account both changes, but it is of course possible to make a bias adjustment corresponding to any one change. . Further, the waveform of the AC voltage that is a component of the bias is not limited to a sine wave, but may be a rectangular wave, a triangular wave, or the like.
[0048]
Further, in place of the counter 10 for detecting a change with time, an ammeter is disposed in the connection path between the bias power source 8 and the charging member 2, and the amount of current applied to the applied bias is measured by the ammeter by the organic photosensitive layer 1b. You may make it measure as a parameter | index of thickness. This utilizes the fact that the amount of current increases as the thickness of the organic photosensitive layer 1b decreases.
[0049]
【The invention's effect】
As described above, according to the image forming apparatus of the present invention, while the maximum peak voltage value of the bias itself is kept constant, the effective voltage value is larger at a low temperature and low humidity than the standard level, On the other hand, it is adjusted to be smaller under high temperature and high humidity. Therefore, under low temperature and low humidity, it is possible to give an effective superimposed bias to the uniformity and charging efficiency of the organic photosensitive layer with reduced chargeability, and the bias is damaged to the organic photosensitive layer. Is not enough to give On the other hand, even at high temperatures and high humidity, it is possible to give a superimposing bias effective for charging uniformity and charging efficiency to an organic photosensitive layer having improved charging properties. Therefore, the quality of the image finally formed on the sheet material is excellent regardless of environmental changes.
[0050]
Also, according to the image forming apparatus of the present invention, the effective voltage value becomes larger as the thickness of the organic photosensitive layer is decreased from the initial level while the maximum peak voltage value of the bias itself is kept constant. Adjusted. For this reason, it is possible to apply an effective superimposing bias to the uniformity and charging efficiency of the organic photosensitive layer whose charging property is gradually lowered due to the decrease in film thickness, and the bias is applied to the organic photosensitive layer. It will not be damaged. Therefore, the quality of the image finally formed on the sheet material is excellent regardless of changes with time.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a main part of an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic diagram of an AC voltage waveform in bias according to the present embodiment.
FIG. 3 is a data table showing an example of a ratio of positive component areas corresponding to environmental changes in bias according to the present embodiment.
FIG. 4 is a schematic diagram showing the correlation between the cumulative number of output sheets and the thickness of the organic photosensitive layer.
FIG. 5 is a data table showing an example of a ratio of positive component regions corresponding to a change with time in bias according to the present embodiment.
FIG. 6 is a flowchart illustrating an image forming operation in the image forming apparatus according to the embodiment.
FIG. 7 is a schematic diagram showing a correlation between temperature, humidity and chargeability of an organic photosensitive layer.
FIG. 8 is a schematic view showing the correlation between the thickness of the organic photosensitive layer and its charging property.
[Explanation of symbols]
1 Photoconductor (image carrier)
1a Conductive tube
1b Organic photosensitive layer
2 Charging member (contact charging member)
2a Conductive substrate
2b Conductive rubber layer
3 Exposure unit
4 Developer
5 Transfer device
6 Cleaning device
7 Fixing device
8 Bias power supply (bias application means)
9 Sensor
10 counters
11 CPU
A Positive component region of AC voltage waveform, which is a component of bias
B Negative component region of AC voltage waveform, which is a component of bias
P sheet material

Claims (6)

An image carrier having an organic photosensitive layer on the surface, a contact charging member that contacts the surface of the image carrier to charge the organic photosensitive layer to a predetermined potential, and a bias in which a DC voltage and an AC voltage are superimposed are generated. And an image forming apparatus provided with a bias applying means for applying to the contact charging member,
A sensor that detects at least one of a temperature or humidity around the image carrier, and a control unit that controls the bias applying unit based on a detected temperature or detected humidity from the sensor,
The control means relates to the detection result with respect to the bias, while maintaining a constant voltage value of the DC voltage and a peak voltage value of the AC voltage, the positive component region and the negative component region in the waveform of the AC voltage. The ratio of the component area having the same polarity as the charged polarity of the image carrier is smaller as the detection temperature or the detection humidity is higher, and the detection temperature or the detection humidity is lower. The image forming apparatus is characterized in that it is set larger according to the above. An image carrier having an organic photosensitive layer on the surface, a contact charging member that contacts the surface of the image carrier to charge the organic photosensitive layer to a predetermined potential, and a bias in which a DC voltage and an AC voltage are superimposed are generated. And an image forming apparatus provided with a bias applying means for applying to the contact charging member,
A thickness index detecting means for detecting an index of the thickness of the organic photosensitive layer, and a control means for controlling the bias applying means based on a detection result from the thickness index detecting means,
The control means calculates a positive component region and a negative component region in the waveform of the AC voltage from the detection result while maintaining the voltage value of the DC voltage and the peak voltage value of the AC voltage constant with respect to the bias. The ratio of the component area having the same polarity as the charged polarity of the image carrier is set larger as the thickness decreases. An image forming apparatus. The image forming apparatus according to claim 2, wherein the thickness index detecting unit detects, as the index, a cumulative number of sheet materials that are formed and output by the image forming apparatus. The image forming apparatus according to claim 2, wherein the thickness index detection unit detects the amount of current of the bias flowing into the contact charging member from the bias application unit as the index. The image forming apparatus according to claim 1, wherein the contact charging member has a roller shape or a brush shape. 6. The image forming apparatus according to claim 1, wherein the organic photosensitive layer is a single layer, and the charging polarity of the image carrier is positive.

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